With a tendency in recent years to promote digitization of information, image processing apparatuses, such as printers and facsimile machines used to output digitized information and scanners used to digitize documents, have become indispensable. In many cases, such image processing apparatuses are provided with capabilities such as an imaging function, an image forming function, and a communication function and configured as a multifunction machine usable as a printer, a facsimile machine, a scanner, and a copier.
Among such image processing apparatuses, one type of printer used to output digitized information uses an inkjet method (hereinafter referred to as an inkjet printer). In the inkjet printer, a recording head ejects ink onto a sheet serving as a recording medium, and thereby an image is formed.
Control of the ink ejection from the recording head is conducted by various means, for example, by a device using a piezoelectric element, a device which heats the ink to generate air bubbles and eject the ink with the resultant pressure, or a device using electrostatic force. The recording head using such an ejection control device is capable of realizing a high-density multi-nozzle structure with relative ease and thus forming a high-definition image on the sheet.
To form a high-quality image by using such a multi-nozzle recording head, it is desirable to uniformly control the ink amounts ejected from the respective nozzles. However, an increase in the number of nozzles, i.e., channels, requires variations in the lengths of the individual wiring used for driving the respective channels. As a result, the multi-nozzle, i.e., multi-channel recording head also experiences variations in drive signal waveform among the channels. The differences in drive signal waveform appear as differences in ejected ink amount. Consequently, therefore, the image quality is degraded.
To address the above issue, it is possible to set different ON resistances for switching elements which control signal application to driving elements for driving the respective channels, and vary the wiring resistance between the driving element and the switching element by channel, thus offsetting changes in impedance due to the variations in the length of the wiring and minimizing the differences in drive signal waveform.
Alternatively, it is possible to provide an impedance changing device on each of multiple signal supply lines for supplying signals to the switching elements on the respective channels, to thereby obtain an effect similar to the above-described effect. Still another method is to provide a charging device which sets, for each of the driving elements on the respective channels, the state of charge of the driving element, to thereby obtain an effect similar to the above-described effect.
In the first method, the wiring resistance between the switching element and the driving element is adjusted for each of the channels. Unlike a case where components to be connected are selected, adjusting the wiring resistance involves, for example, adjusting the length of the wires and adjusting the components of the material forming the wiring line. Therefore, the method complicates both design and production, and causes an increase in cost.
Further, in the second and third methods, an extra device such as an impedance changing device and a charging device must be provided, causing an increase in device size and cost.